Electrical insulation film

ABSTRACT

Certain embodiments of the present technology provide a capacitor film comprising a polypropylene material. The capacitor film comprises xylene solubles of at least 0.5 percent by weight. In certain embodiments the xylene solubles are in a range of 0.5 to 1.5 percent by weight. The film also comprises a crystalline fraction melting in the temperature range of 200° C. to 105° C. determined by stepwise isothermal segregation technique. The crystalline fraction comprises a part, the part representing at least 10 percent by weight of said crystalline fraction, and wherein the part melts at a melting rate of 10° C./min. Certain embodiments present a capacitor film where the part melts at or below 140° C. In other embodiments, the said part melts at or below the temperature T=Tm−3° C., wherein Tm is the melting temperature of the capacitor film and/or the polypropylene material, and the part represents at least 45 percent by weight of the crystalline fraction.

RELATED APPLICATIONS

This application is a continuation of International Application SerialNo. PCT/EP2007/006056 (International Publication Number WO 2008/006529A1), having an International filing date of Jul. 9, 2007 entitled“Electrical Insulation Film”. International Application No.PCT/EP2007/006056 claimed priority benefits, in turn, from EuropeanPatent Application No. 06014270.0 filed Jul. 10, 2006. InternationalApplication No. PCT/EP2007/006056 and European Patent Application No.06014270.0 are hereby incorporated by reference herein in theirentireties.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable]

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable]

BACKGROUND OF THE INVENTION

The present technology relates to electrical insulation films, inparticular capacitor films, and their use.

Capacitor films must withstand extreme conditions like high temperaturesand high electrical breakdown strength. Additionally it is appreciatedthat capacitor films possess good mechanical properties like a highstiffness. Up to now there is the prevailing opinion in the technicalfield of capacitor technology that high electrical breakdown strengthcan be only achieved with a low level of electrical conduction caused byresidual metals such as titanium, aluminium and boron. Howevertraditional polypropylenes produced with a Ziegler-Natta catalyst arecontaminated with high amounts of residual catalyst components. Toachieve the desired very low levels of impurities to make thepolypropylene suitable for capacitor films, the polypropylenes must betroublesome washed, a process which is time consuming andcost-intensive. To overcome the washing step polypropylenes produced inthe presence of supported single-site catalysts have been developed, asfor instance described in WO 02/16455 A1, with low levels of impuritiesincluding metallic and non-metallic impurities, like aluminium,titanium, silicon, and halogen (such as Cl and F). However to achievethis goal of low levels of impurities the process conditions must becontrolled very carefully. Moreover such polypropylenes have thedrawback that they cannot be processed in a stable way. In particularfilms based on polypropylenes produced in the presence of supportedsingle-site catalysts suffer from sagging and break easily whenmanufactured.

Therefore the object of the present technology is to provide a capacitorfilm with a high temperature resistance and high electrical breakdownstrength paired with good mechanical properties, in particular a highstiffness.

BRIEF SUMMARY OF THE INVENTION

The present technology is based on the finding that an improved balanceof high thermal resistance, high electrical breakdown strength and goodmechanical properties can be accomplished by introducing a specificdegree of short-chain branching in combination with a specific amount ofnon-crystalline areas. It is been in particular found out that the goodproperties can be achieved independently from the amount of impuritiespresent, i.e. whether the polypropylene comprises rather high amounts ofaluminium, titanium, silicon, halogen (such as Cl and F) and/or boron.

Accordingly, in a first embodiment of the present technology, the objectoutlined above is solved by providing a electrical insulation film, likea capacitor film, comprising a polypropylene wherein the film and/or thepolypropylene has/have

a) xylene solubles (XS) of at least 0.5 wt.-% and

b) a strain hardening index (SHI@1 s⁻¹) of at least 0.15 measured at adeformation rate dε/dt of 1.00 s⁻¹ at a temperature of 180° C., whereinthe strain hardening index (SHI) is defined as the slope of thelogarithm to the basis 10 of the tensile stress growth function (lg(η_(E) ⁺)) as function of the logarithm to the basis 10 of the Henckystrain (lg (ε)) in the range of the Hencky strains between 1 and 3.

Surprisingly, it has been found that capacitor films comprising apolypropylene with such characteristics have superior propertiescompared to the films known in the art. Especially, the inventivecapacitor films have high values of electrical breakdown strength alsoin case relatively high amounts of impurities are present in the film.Thus no troublesome washing steps are necessary as by polypropylenesknown in the art. Moreover the capacitor films according the presenttechnology have in addition a high temperature resistance and areobtainable at high process stability and low process temperature.Moreover and surprisingly the inventive film has in addition goodmechanical properties as a high stiffness expressed in tensile modulus.Additionally it has been observed that the new capacitor films accordingto the present technology show a significant increase of electricalbreakdown strength with increasing the draw ratio.

Certain embodiments of the present technology provide a capacitor filmcomprising a polypropylene material. The capacitor film comprises xylenesolubles of at least 0.5 percent by weight. In certain embodiments thexylene solubles are in a range of 0.5 to 1.5 percent by weight. The filmalso comprises a crystalline fraction melting in the temperature rangeof 200° C. to 105° C. determined by stepwise isothermal segregationtechnique. The crystalline fraction comprises a part, the partrepresenting at least 10 percent by weight of said crystalline fraction,and wherein the part melts at a melting rate of 10° C./min. Certainembodiments present a capacitor film where the part melts at or below140° C. In other embodiments, the said part melts at or below thetemperature T=Tm−3° C., wherein Tm is the melting temperature of thecapacitor film and/or the polypropylene material, and the partrepresents at least 45 percent by weight of the crystalline fraction.

In certain embodiments of the present technology, the film has a strainhardening index of at least 0.15 measured at a deformation rate of 1.00s⁻¹ at a temperature of 180° C. The strain hardening index can bedefined as the slope of the logarithm to the basis 10 of the tensilestress growth function as function of the logarithm to the basis 10 ofthe Hencky strain for the range of the Hencky strains between 1 and 3.

Certain embodiments of the presently described technology provide amethod of using the capacitor film described in a capacitor. In certainembodiments, a capacitor is provided, the capacitor having at least onelayer comprising the capacitor film described herein.

Certain embodiments provide a process or a method for the preparation ofthe capacitor film described herein, involving the step of forming thepolypropylene material is formed into a film. In certain embodiments,the polypropylene material is formed into a cast film. In certainembodiments, the film is biaxially oriented. In certain embodiments ofthe process of the present technology, the polypropylene is preparedusing a catalyst system of low porosity, the catalyst system comprisinga symmetric catalyst, wherein the catalyst system has a porosity of lessthan 1.40 ml/g [measured according to DIN 66135]. The catalyst systemcan be a non-silica supported system. The catalyst system can also havea porosity below the detection limit as defined according to DIN 66135.In certain embodiments, the catalyst system has a surface area of lessthan 25 m²/g [measured according to ISO 9277].

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a graph depicting the determination of a Strain HardeningIndex of “A” at a strain rate of 0.1 s⁻¹ (SHI@0.1 s⁻¹).

FIG. 2 is a graph depicting the deformation rate versus strainhardening.

FIG. 3 is a graph depicting catalyst particle size distribution viaCoulter counter.

FIG. 4 is a graph of the electrical breakdown strength of difficultyoriented specimen.

FIG. 5 is a graph of SIST Curve E 1 (for a 6.76 milligram sample).

FIG. 6 is a graph of SIST Curve CE 1 (for a 5.21 milligram sample).

FIG. 7 is a graph of SIST Curve CE 2 (for a 7.27 milligram sample).

DETAILED DESCRIPTION OF THE INVENTION

A first requirement of the first embodiment of the present technology isthat the capacitor film comprising a polypropylene and/or thepolypropylene itself has/have xylene solubles of some extent, i.e. of atleast 0.50 wt.-%. Xylene solubles are the part of the polymer soluble incold xylene determined by dissolution in boiling xylene and letting theinsoluble part crystallize from the cooling solution (for the method seebelow in the experimental part). The xylene solubles fraction containspolymer chains of low stereo-regularity and is an indication for theamount of non-crystalline areas.

Preferably, the polypropylene component of the film has xylene solublesof more than 0.60 wt.-%. On the other hand, the amount of xylenesolubles should not be too high since they represent a potentialcontamination risk. Accordingly it is preferred that the xylene solublesare not more than 1.50 wt.-%, still more preferably not more than 1.35wt.-% and yet more preferably not more than 1.00 wt.-%. In preferredembodiments the xylene solubles are in the range of 0.50 to 1.50 wt.-%,yet more preferably in the range of 0.60 to 1.35 wt.-%, and still morepreferably in the range of 0.60 to 1.00 wt.-%.

Preferably, the capacitor film has xylene solubles of more than 0.60wt.-%. Even more preferred, the capacitor film has xylene solubles ofnot more than 1.50 wt.-%, more preferably of not more than 1.35 wt.-%.In particular, the film has xylene solubles in the range of 0.50 wt.-%to 1.35 wt. %, even more preferably 0.60 wt.-% to 1.35 wt.-%, and mostpreferably 0.60 wt.-% to 1.00 wt.-%.

Furthermore the capacitor film and/or the polypropylene component of thefilm according to the present technology is/are characterized inparticular by extensional melt flow properties. The extensional flow, ordeformation that involves the stretching of a viscous material, is thedominant type of deformation in converging and squeezing flows thatoccur in typical polymer processing operations. Extensional melt flowmeasurements are particularly useful in polymer characterization becausethey are very sensitive to the molecular structure of the polymericsystem being tested. When the true strain rate of extension, alsoreferred to as the Hencky strain rate, is constant, simple extension issaid to be a “strong flow” in the sense that it can generate a muchhigher degree of molecular orientation and stretching than flows insimple shear. As a consequence, extensional flows are very sensitive tocrystallinity and macro-structural effects, such as short-chainbranching, and as such can be far more descriptive with regard topolymer characterization than other types of bulk rheologicalmeasurement which apply shear flow.

Accordingly one requirement of the present technology is that thecapacitor film and/or the polypropylene component of the capacitor filmhas/have a strain hardening index (SHI@1 s⁻¹) of at least 0.15, morepreferred of at least 0.20, yet more preferred the strain hardeningindex (SHI@1 s⁻¹) is in the range of 0.15 to 0.30, like 0.15 to below0.30, and still yet more preferred in the range of 0.15 to 0.29. In afurther embodiment it is preferred that the capacitor film and/or thepolypropylene component of the capacitor film has/have a strainhardening index (SHI@1 s⁻¹) in the range of 0.20 to 0.30, like 0.20 tobelow 0.30, more preferred in the range of 0.20 to 0.29.

The strain hardening index is a measure for the strain hardeningbehavior of the polypropylene melt. Moreover values of the strainhardening index (SHI@1 s⁻¹) of more than 0.10 indicate a non-linearpolymer, i.e. a short-chain branched polymer. In the present technology,the strain hardening index (SHI@1 s⁻¹) is measured by a deformation ratedε/dt of 1.00 s⁻¹ at a temperature of 180° C. for determining the strainhardening behavior, wherein the strain hardening index (SHI@1 s⁻¹) isdefined as the slope of the tensile stress growth function η_(E) ⁺ as afunction of the Hencky strain ε on a logarithmic scale between 1.00 and3.00 (see FIG. 1). Thereby the Hencky strain ε is defined by the formulaε={dot over (ε)}_(H)·t, wherein the Hencky strain rate {dot over(ε)}_(H) is defined by the formula:

${{\overset{.}{ɛ}}_{H} = \frac{2 \cdot \Omega \cdot R}{L_{0}}};$with

“L₀” is the fixed, unsupported length of the specimen sample beingstretched which is equal to the centerline distance between the masterand slave drums;

“R” is the radius of the equi-dimensional windup drums; and

“Ω” is a constant drive shaft rotation rate.

In turn the tensile stress growth function η_(E) ⁺ is defined by theformula:

${{\eta_{E}^{+}(ɛ)} = \frac{F(ɛ)}{{\overset{.}{ɛ}}_{H} \cdot {A(ɛ)}}};{with}$T(ɛ) = 2 ⋅ R ⋅ F(ɛ); and${{A(ɛ)} = {A_{0} \cdot \left( \frac{d\,_{S}}{d\,_{M}} \right)^{2/3} \cdot {\exp\left( {- ɛ} \right)}}};{wherein}$

-   -   the Hencky strain rate {dot over (ε)}_(H) is defined as for the        Hencky strain ε;    -   “F” is the tangential stretching force;    -   “R” is the radius of the equi-dimensional windup drums;    -   “T” is the measured torque signal, related to the tangential        stretching force “F”;    -   “A” is the instantaneous cross-sectional area of a stretched        molten specimen;    -   “A₀” is the cross-sectional area of the specimen in the solid        state (i.e. prior to melting);    -   “d_(s)” is the solid state density; and    -   “d_(M)” the melt density of the polymer.

Another physical parameter which is sensitive to crystallinity andmacro-structural effects is the so-called multi-branching index (MBI),as will be explained below in further detail.

Similarly to the measurement of SHI@1 s⁻¹, a strain hardening index(SHI) can be determined at different strain rates. A strain hardeningindex (SHI) is defined as the slope of the logarithm to the basis 10 ofthe tensile stress growth function η_(E) ⁺, lg(η_(E) ⁺), as function ofthe logarithm to the basis 10 of the Hencky strain ε, lg(ε), betweenHencky strains 1.00 and 3.00 at a temperature of 180° C., wherein aSHI@0.1 s−1 is determined with a deformation rate {dot over (ε)}_(H) of0.10 s⁻¹, a SHI@0.3 s−1 is determined with a deformation rate {dot over(ε)}_(H) of 0.30 s⁻¹, a SHI@3.0 s−1 is determined with a deformationrate {dot over (ε)}_(H) of 3.00 s⁻¹, a SHI@10.0 s−1 is determined with adeformation rate {dot over (ε)}_(H) of 10.0 S⁻¹. In comparing the strainhardening index (SHI) at those five strain rates {dot over (ε)}_(H) of0.10, 0.30, 1.00, 3.00 and 10.00 s⁻¹, the slope of the strain hardeningindex (SHI) as function of the logarithm on the basis 10 of {dot over(ε)}_(H), lg({dot over (ε)}_(H)), is a characteristic measure forshort-chain-branching. Therefore, a multi-branching index (MBI) isdefined as the slope of the strain hardening index (SHI) as a functionof lg({dot over (ε)}_(H)), i.e. the slope of a linear fitting curve ofthe strain hardening index (SHI) versus lg({dot over (ε)}_(H)) applyingthe least square method, preferably the strain hardening index (SHI) isdefined at deformation rates {dot over (ε)}_(H) between 0.05 s⁻¹ and20.00 s⁻¹, more preferably between 0.10 s⁻¹ and 10.00 s⁻¹, still morepreferably at the deformations rates 0.10, 0.30, 1.00, 3.00 and 10.00s⁻¹. Yet more preferably the SHI-values determined by the deformationsrates 0.10, 0.30, 1.00, 3.00 and 10.00 s⁻¹ are used for the linear fitaccording to the least square method when establishing themulti-branching index (MBI).

Preferably, the polypropylene component of the capacitor film has amulti-branching index (MBI) of at least 0.10, more preferably at least0.15, yet more preferably the multi-branching index (MBI) is in therange of 0.10 to 0.30. In a preferred embodiment the polypropylene has amulti-branching index (MBI) in the range of 0.15 to 0.30.

The polypropylene component of the film of the present technology ischaracterized by the fact that the strain hardening index (SHI)increases to some extent with the deformation rate {dot over (ε)}_(H)(i.e. short-chain branched polypropylenes), i.e. a phenomenon which isnot observed in linear polypropylenes. Single branched polymer types (socalled Y polymers having a backbone with a single long side-chain and anarchitecture which resembles a “Y”) or H-branched polymer types (twopolymer chains coupled with a bridging group and a architecture whichresemble an “H”) as well as linear polymers do not show such arelationship, i.e. the strain hardening index (SHI) is not influenced bythe deformation rate (see FIG. 2). Accordingly, the strain hardeningindex (SHI) of known polymers, in particular known polypropylenes, doesnot increase with increase of the deformation rate (dε/dt). Industrialconversion processes which imply elongational flow operate at very fastextension rates. Hence the advantage of a material which shows morepronounced strain hardening (measured by the strain hardening index SHI)at high strain rates becomes obvious. The faster the material isstretched, the higher the strain hardening index and hence the morestable the material will be in conversion.

When measured on capacitor film, the multi-branching index (MBI) is atleast 0.10, more preferably of at least 0.15, yet more preferably themulti-branching index (MBI) is in the range of 0.10 to 0.30. In apreferred embodiment the capacitor film has a multi-branching index(MBI) in the range of 0.15 to 0.30.

Additionally the polypropylene of the capacitor film of the presenttechnology has preferably a branching index g′ of less than 1.00. Stillmore preferably the branching index g′ is more than 0.7. Thus it ispreferred that the branching index g′ of the polypropylene is in therange of more than 0.7 to below 1.0, more preferred in the range of morethan 0.7 to 0.95, still more preferred in the range of 0.75 to 0.95. Thebranching index g′ defines the degree of branching and correlates withthe amount of branches of a polymer. The branching index g′ is definedas g′=[IV]_(br)/[IV]_(lin) in which g′ is the branching index, [IV_(br)]is the intrinsic viscosity of the branched polypropylene and [IV]_(lin)is the intrinsic viscosity of the linear polypropylene having the sameweight average molecular weight (within a range of ±3%) as the branchedpolypropylene. Thereby, a low g′-value is an indicator for a highbranched polymer. In other words, if the g′-value decreases, thebranching of the polypropylene increases. Reference is made in thiscontext to B. H. Zimm and W. H. Stockmeyer, J. Chem. Phys. 17, 1301(1949). This document is herewith included by reference.

The intrinsic viscosity needed for determining the branching index g′ ismeasured according to DIN ISO 1628/1, October 1999 (in decalin at 135°C.).

When measured on the capacitor film, the branching index g′ ispreferably in the range of more than 0.7 to below 1.0.

For further information concerning the measuring methods applied toobtain the relevant data for the branching index g′, the tensile stressgrowth function η_(E) ⁺, the Hencky strain rate {dot over (ε)}_(H), theHencky strain ε and the multi-branching index (MBI) it is referred tothe example section.

Moreover it is preferred that the capacitor film according to thepresent technology is further specified by its lamellar thicknessdistribution. It has been recognized that higher electrical breakdownstrength is achievable in case the polymer comprises rather high amountsof thin lamellae. Thus the acceptance of the film as a capacitor film isindependent from the amounts of impurities present in the polypropylenebut from its crystalline properties. The stepwise isothermal segregationtechnique (SIST) provides a possibility to determine the lamellarthickness distribution. Rather high amounts of polymer fractionscrystallizing at lower temperatures indicate a rather high amount ofthin lamellae. Thus the inventive capacitor film and/or thepolypropylene of the film comprise(s) a crystalline fractioncrystallizing in the temperature range of 200 to 105° C. determined bystepwise isothermal segregation technique (SIST), wherein saidcrystalline fraction comprises a part which during subsequent-melting ata melting rate of 10° C./min melts at or below 140° C. and said partrepresents at least 10 wt %, more preferably at least 15 wt-%, stillmore preferably at least 20 wt-% and yet more preferably at least 25wt-% of said crystalline fraction. Alternatively, the inventivecapacitor film and/or the polypropylene of the film comprise(s) acrystalline fraction crystallizing in the temperature range of 200 to105° C. determined by stepwise isothermal segregation technique (SIST),wherein said crystalline fraction comprises a part which duringsubsequent melting at a melting rate of 10° C./min melts at or below thetemperature T=Tm−3° C., wherein Tm is the melting temperature of thecapacitor film and/or the polypropylene material, and said partrepresents at least 45 wt-%, more preferably at least 50 wt-%, yet morepreferably at least 55 wt-%, of said crystalline fraction. Furtherdetails about SIST are provided below in the examples.

In addition it is preferred that the crystalline fraction whichcrystallizes between 200 to 105° C. determined by stepwise isothermalsegregation technique (SIST) is at least 90 wt.-% of the total filmand/or the total polypropylene, more preferably at least 95 wt.-% of thetotal film and/or the total polypropylene and yet more preferably 98wt.-% of the total film and/or the total polypropylene.

In a second embodiment the present technology provides an electricalinsulation film, like a capacitor film, comprising a polypropylene,wherein the film and/or the polypropylene of the film:

a) has/have xylene solubles (XS) of at least 0.5 wt.-%; and

b) comprise(s) a crystalline fraction crystallizing in the temperaturerange of 200 to 105° C. determined by stepwise isothermal segregationtechnique (SIST), wherein said crystalline fraction comprises a partwhich during subsequent-melting at a melting rate of 10° C./min melts ator below 140° C. and said part represents at least 10 wt %, morepreferably at least 20 wt-%, of said crystalline fraction.

Alternatively, the second embodiment the present technology provides anelectrical insulation film, like a capacitor film, comprising apolypropylene, wherein the film and/or the polypropylene of the film:

a) has/have xylene solubles (XS) of at least 0.5 wt.-%; and

b) comprise(s) a crystalline fraction crystallizing in the temperaturerange of 200 to 105° C. determined by stepwise isothermal segregationtechnique (SIST), wherein said crystalline fraction comprises a partwhich during subsequent melting at a melting rate of 10° C./min melts ator below the temperature T=Tm−3° C., wherein Tm is the meltingtemperature, and said part represents at least 45 wt-%, more preferablyat least 50 wt-%, yet more preferably at least 55 wt-%, of saidcrystalline fraction.

Surprisingly, it has been found that capacitor films comprising apolypropylene with such characteristics have superior propertiescompared to the films known in the art. Especially, the inventivecapacitor films have high values of electrical breakdown strength alsoin case relatively high amounts of impurities are present in the film.Thus no troublesome washing steps are necessary as by polypropylenesknown in the art. Moreover the capacitor films according to the presenttechnology have in addition a high temperature resistance and areobtainable at high process stability and low process temperature.Moreover and surprisingly the inventive film has in addition goodmechanical properties as a high stiffness expressed in tensile modulus.Additionally it has been observed that the new capacitor films accordingto the present technology show a significant increase of electricalbreakdown strength with increasing the draw ratio.

A first requirement of the second embodiment of the present technologyis that the capacitor film comprising a polypropylene and/or thepolypropylene itself has/have xylene solubles of some extent, i.e. of atleast 0.50 wt.-%. Xylene solubles are the part of the polymer soluble incold xylene determined by dissolution in boiling xylene and letting theinsoluble part crystallize from the cooling solution (for the method seebelow in the experimental part). The xylene solubles fraction containspolymer chains of low stereo-regularity and is an indication for theamount of non-crystalline areas.

Preferably, the polypropylene component of the film has xylene solublesof more than 0.60 wt.-%. On the other hand, the amount of xylenesolubles should not be too high since they represent a potentialcontamination risk. Accordingly it is preferred that the xylene solublesare not more than 1.50 wt.-%, still more preferably not more than 1.35wt.-% and yet more preferably not more than 1.00 wt.-%. In preferredembodiments the xylene solubles are in the range of 0.50 to 1.50 wt.-%,yet more preferably in the range of 0.60 to 1.35 wt.-%, and still morepreferably in the range of 0.60 to 1.00 wt.-%.

Preferably, the capacitor film has xylene solubles of not more than 1.50wt.-%, more preferably of not more than 1.35 wt.-%. More preferably, thefilm has xylene solubles in the range of 0.50 wt.-% to 1.35 wt. %, evenmore preferably 0.60 wt.-% to 1.35 wt.-%, and most preferably 0.60 wt.-%to 1.00 wt.-%.

The capacitor film according to the present technology is furtherspecified by its lamellar thickness distribution. It has been recognizedthat higher electrical breakdown strength is achievable in case thepolymer comprises rather high amounts of thin lamellae. Thus theacceptance of the film as a capacitor film is independent from theamounts of impurities present in the polypropylene but from itscrystalline properties. The stepwise isothermal segregation technique(SIST) provides a possibility to determine the lamellar thicknessdistribution. Rather high amounts of polymer fractions crystallizing atlower temperatures indicate a rather high amount of thin lamellae. Thusthe inventive capacitor film and/or the polypropylene of the filmcomprise(s) a crystalline fraction crystallizing in the temperaturerange of 200 to 105° C. determined by stepwise isothermal segregationtechnique (SIST), wherein said crystalline fraction comprises a partwhich during subsequent-melting at a melting rate of 10° C./min melts ator below 140° C. and said part represents at least 10 wt %, morepreferably at least 15 wt-%, still more preferably at least 20 wt-% andyet more preferably at least 25 wt-% of said crystalline fraction.Further details about SIST are provided below in the examples.

In addition it is preferred that the crystalline fraction whichcrystallizes between 200 to 105° C. determined by stepwise isothermalsegregation technique (SIST) is at least 90 wt.-% of the total filmand/or the total polypropylene, more preferably at least 95 wt.-% of thetotal film and/or the total polypropylene and yet more preferably 98wt.-% of the total film and/or the total polypropylene.

Moreover, the capacitor film and/or the polypropylene component of thefilm according to the present technology is/are preferably characterizedby extensional melt flow properties. The extensional flow, ordeformation that involves the stretching of a viscous material, is thedominant type of deformation in converging and squeezing flows thatoccur in typical polymer processing operations. Extensional melt flowmeasurements are particularly useful in polymer characterization becausethey are very sensitive to the molecular structure of the polymericsystem being tested. When the true strain rate of extension, alsoreferred to as the Hencky strain rate, is constant, simple extension issaid to be a “strong flow” in the sense that it can generate a muchhigher degree of molecular orientation and stretching than flows insimple shear. As a consequence, extensional flows are very sensitive tocrystallinity and macro-structural effects, such as short-chainbranching, and as such can be far more descriptive with regard topolymer characterization than other types of bulk rheologicalmeasurement which apply shear flow.

Accordingly one requirement of the present technology is that thecapacitor film and/or the polypropylene component of the capacitor filmhas/have a strain hardening index (SHI@1 s⁻¹) of at least 0.15, morepreferred of at least 0.20, yet more preferred the strain hardeningindex (SHI@1 s⁻¹) is in the range of 0.15 to 0.30, like 0.15 to below0.30, and still yet more preferred in the range of 0.15 to 0.29. In afurther embodiment it is preferred that the capacitor film and/or thepolypropylene component of the capacitor film has/have a strainhardening index (SHI@1 s⁻¹) in the range of 0.20 to 0.30, like 0.20 tobelow 0.30, more preferred in the range of 0.20 to 0.29.

The strain hardening index is a measure for the strain hardeningbehavior of the polypropylene melt. Moreover values of the strainhardening index (SHI@1 s⁻¹) of more than 0.10 indicate a non-linearpolymer, i.e. a short-chain branched polymer. In the present technology,the strain hardening index (SHI@1 s⁻¹) is measured by a deformation ratedε/dt of 1.00 s⁻¹ at a temperature of 180° C. for determining the strainhardening behavior, wherein the strain hardening index (SHI@1 s⁻¹) isdefined as the slope of the tensile stress growth function η_(E) ⁺ as afunction of the Hencky strain ε on a logarithmic scale between 1.00 and3.00 (see FIG. 1). Thereby the Hencky strain ε is defined by the formulaε={dot over (ε)}_(H)·t, wherein the Hencky strain rate {dot over(ε)}_(H) is defined by the formula:

${{\overset{.}{ɛ}}_{H} = \frac{2 \cdot \Omega \cdot R}{L_{0}}};$with

-   -   “L₀” is the fixed, unsupported length of the specimen sample        being stretched which is equal to the centerline distance        between the master and slave drums;    -   “R” is the radius of the equi-dimensional windup drums; and    -   “Ω” is a constant drive shaft rotation rate.

In turn the tensile stress growth function η_(E) ⁺ is defined by theformula:

${{\eta_{E}^{+}(ɛ)} = \frac{F(ɛ)}{{\overset{.}{ɛ}}_{H} \cdot {A(ɛ)}}};{with}$T(ɛ) = 2 ⋅ R ⋅ F(ɛ); and${{A(ɛ)} = {A_{0} \cdot \left( \frac{d\,_{S}}{d\,_{M}} \right)^{2/3} \cdot {\exp\left( {- ɛ} \right)}}};{wherein}$

-   -   the Hencky strain rate {dot over (ε)}_(H) is defined as for the        Hencky strain ε;    -   “F” is the tangential stretching force;    -   “R” is the radius of the equi-dimensional windup drums;    -   “T” is the measured torque signal, related to the tangential        stretching force “F”;    -   “A” is the instantaneous cross-sectional area of a stretched        molten specimen;    -   “A₀” is the cross-sectional area of the specimen in the solid        state (i.e. prior to melting);    -   “d_(s)” is the solid state density; and    -   “d_(M)” the melt density of the polymer.

Another physical parameter which is sensitive to crystallinity andmacro-structural effects is the so-called multi-branching index (MBI),as will be explained below in further detail.

Concerning to the determination of the multi-branching index (MBI) it isreferred to the first embodiment of the present technology.

Preferably, the polypropylene component of the capacitor film has amulti-branching index (MBI) of at least 0.10, more preferably at least0.15, yet more preferably the multi-branching index (MBI) is in therange of 0.10 to 0.30. In a preferred embodiment the polypropylene has amulti-branching index (MBI) in the range of 0.15 to 0.30.

The polypropylene component of the capacitor film of the presenttechnology is characterized by the fact that the strain hardening index(SHI) increases to some extent with the deformation rate {dot over(ε)}_(H) (i.e. short-chain branched polypropylenes), i.e. a phenomenonwhich is not observed in linear polypropylenes. Single branched polymertypes (so called Y polymers having a backbone with a single longside-chain and an architecture which resembles a “Y”) or H-branchedpolymer types (two polymer chains coupled with a bridging group and aarchitecture which resemble an “H”) as well as linear polymers do notshow such a relationship, i.e. the strain hardening index (SHI) is notinfluenced by the deformation rate (see FIG. 2). Accordingly, the strainhardening index (SHI) of known polymers, in particular knownpolypropylenes, does not increase with increase of the deformation rate(dε/dt). Industrial conversion processes which imply elongational flowoperate at very fast extension rates. Hence the advantage of a materialwhich shows more pronounced strain hardening (measured by the strainhardening index SHI) at high strain rates becomes obvious. The fasterthe material is stretched, the higher the strain hardening index andhence the more stable the material will be in conversion.

When measured on the capacitor film, the multi-branching index (MBI) isat least 0.10, more preferably of at least 0.15, yet more preferably themulti-branching index (MBI) is in the range of 0.10 to 0.30. In apreferred embodiment the film has a multi-branching index (MBI) in therange of 0.15 to 0.30.

Additionally the polypropylene of the capacitor film of the presenttechnology has preferably a branching index g′ of less than 1.00. Stillmore preferably the branching index g′ is more than 0.7. Thus it ispreferred that the branching index g′ of the polypropylene is in therange of more than 0.7 to below 1.0, more preferred in the range of morethan 0.7 to 0.95, still more preferred in the range of 0.75 to 0.95. Thebranching index g′ defines the degree of branching and correlates withthe amount of branches of a polymer. The branching index g′ is definedas g′=[IV]_(br)/[IV]_(lin) in which g′ is the branching index, [IV_(br)]is the intrinsic viscosity of the branched polypropylene and [IV]_(lin)is the intrinsic viscosity of the linear polypropylene having the sameweight average molecular weight (within a range of ±3%) as the branchedpolypropylene. Thereby, a low g′-value is an indicator for a highbranched polymer. In other words, if the g′-value decreases, thebranching of the polypropylene increases. Reference is made in thiscontext to B. H. Zimm and W. H. Stockmeyer, J. Chem. Phys. 17, 1301(1949). This document is herewith included by reference.

The intrinsic viscosity needed for determining the branching index g′ ismeasured according to DIN ISO 1628/1, October 1999 (in decalin at 135°C.).

When measured on the capacitor film, the branching index g′ ispreferably in the range of more than 0.7 to below 1.0.

For further information concerning the measuring methods applied toobtain the relevant data for the branching index g′, the tensile stressgrowth function η_(E) ⁺, the Hencky strain rate {dot over (ε)}_(H), theHencky strain ε and the multi-branching index (MBI) it is referred tothe example section.

The further features mentioned below apply to both embodiments, i.e. thefirst and the second embodiment as defined above.

The molecular weight distribution (MWD) (also determined herein aspolydispersity) is the relation between the numbers of molecules in apolymer and the individual chain length. The molecular weightdistribution (MWD) is expressed as the ratio of weight average molecularweight (M_(w)) and number average molecular weight (M_(n)). The numberaverage molecular weight (M_(n)) is an average molecular weight of apolymer expressed as the first moment of a plot of the number ofmolecules in each molecular weight range against the molecular weight.In effect, this is the total molecular weight of all molecules dividedby the number of molecules. In turn, the weight average molecular weight(M_(w)) is the first moment of a plot of the weight of polymer in eachmolecular weight range against molecular weight.

The number average molecular weight (M_(n)) and the weight averagemolecular weight (M_(w)) as well as the molecular weight distribution(MWD) are determined by size exclusion chromatography (SEC) using WatersAlliance GPCV 2000 instrument with online viscometer. The oventemperature is 140° C. Trichlorobenzene is used as a solvent (ISO16014).

It is preferred that the capacitor film of the present technologycomprises a polypropylene which has a weight average molecular weight(M_(w)) from 10,000 to 2,000,000 g/mol, more preferably from 20,000 to1,500,000 g/mol.

The number average molecular weight (M_(n)) of the polypropylene ispreferably in the range of 5,000 to 750,000 g/mol, more preferably from10,000 to 750,000 g/mol.

As a broad molecular weight distribution (MWD) improves theprocessability of the polypropylene the molecular weight distribution(MWD) is preferably up to 20.00, more preferably up to 10.00, still morepreferably up to 8.00. However a rather broad molecular weightdistribution simulates sagging. Therefore, in an alternative embodimentthe molecular weight distribution (MWD) is preferably between 1.00 to8.00, still more preferably in the range of 1.00 to 4.00, yet morepreferably in the range of 1.00 to 3.50.

Furthermore, it is preferred that the polypropylene component of thefilm of the present technology has a melt flow rate (MFR) given in aspecific range. The melt flow rate mainly depends on the averagemolecular weight. This is due to the fact that long molecules render thematerial a lower flow tendency than short molecules. An increase inmolecular weight means a decrease in the MFR-value. The melt flow rate(MFR) is measured in g/10 min of the polymer discharged through adefined die under specified temperature and pressure conditions and themeasure of viscosity of the polymer which, in turn, for each type ofpolymer is mainly influenced by its molecular weight but also by itsdegree of branching. The melt flow rate measured under a load of 2.16 kgat 230° C. (ISO 1133) is denoted as MFR₂. Accordingly, it is preferredthat in the present technology the capacitor film comprises apolypropylene which has an MFR₂ up to 10.00 g/10 min, more preferably upto 6.00 g/10 min. In another preferred embodiment the polypropylene hasMFR₂ up to 4 g/10 min. A preferred range for the MFR₂ is 1.00 to 10.00g/10 min, more preferably in the range of 1.00 to 8.00 g/10 min, yetmore preferably in the range of 1.00 to 6.00 g/10 min.

As cross-linking has a detrimental effect on the extensional flowproperties it is preferred that the polypropylene according to thepresent technology is non-cross-linked.

More preferably, the polypropylene of the instant technology isisotactic. Thus the polypropylene of the film according to the presenttechnology shall have a rather high isotacticity measured by meso pentadconcentration (also referred herein as pentad concentration), i.e.higher than 91%, more preferably higher than 93%, still more preferablyhigher than 94% and most preferably higher than 95%. On the other handpentad concentration shall be not higher than 99.5%. The pentadconcentration is an indicator for the narrowness in the regularitydistribution of the polypropylene and measured by NMR-spectroscopy.

In addition, it is preferred that the polypropylene of the capacitorfilm has a melting temperature Tm of higher than 148° C., more preferredhigher than 150° C. In a preferred embodiment, melting temperature Tm ofthe polypropylene component is higher than 148° C. but below 156° C. Themeasuring method for the melting temperature Tm is discussed in theexample section.

The melting temperature Tm of the capacitor film is preferably at least148° C., more preferably at least 150° C. In a preferred embodiment, themelting temperature Tm of the capacitor film is higher than 150° C. butbelow 160° C.

The capacitor film according to the present technology is preferablybiaxially oriented. Still more preferably the capacitor film is inmachine and transverse direction stretchable up to a draw ratio of atleast 3.5 without breaking, more preferably of at least 4.0 withoutbreaking. In a preferred embodiment the capacitor film according to thepresent technology has a draw ratio in machine and transverse directionof at least 3.5, more preferably of at least 4.0. The length of thesample increases during stretching in longitudinal direction and thedraw ratio in longitudinal direction calculates from the ratio ofcurrent length over original sample length. Subsequently, the sample isstretched in transverse direction where the width of the sample isincreasing. Hence, the draw ratio calculates from the current width ofthe sample over the original width of the sample.

Such rather high tensile modulus at a draw ratio of 4 in machinedirection and a draw ratio of 4 in transverse direction is appreciatedsince biaxially oriented polypropylene films commercially are stretchedwith a draw ratio of 4 to 6 in machine direction and with a draw ratioof 5 to 8 in transverse direction.

Preferably, the polypropylene component of the film of the presenttechnology has a tensile modulus of at least 800 MPa, measured accordingto ISO 527-3 at a cross head speed of 1 mm/min. More preferably, thepolypropylene component has a tensile modulus of at least 850 MPa, evenmore preferably 900 MPa, and yet more preferably at least 1000 MPa.

Preferably, the biaxially oriented polypropylene film of the presenttechnology has a tensile modulus of at least 1800 MPa at a draw ratio of4 in machine direction and a draw ratio of 4 in transverse direction,wherein the tensile modulus is measured according to ISO 527-3 at across head speed of 1 mm/min. More preferably, the polypropylene filmhas a tensile modulus of at least 1900 MPa, even more preferably 1950MPa, and most preferably at least 2200 MPa at a draw ratio of 4 inmachine direction and a draw ratio of 4 in transverse direction.

In a preferred embodiment, the film has a stretching stress of at least2.5 MPa in machine direction and at least 2.5 MPa in transversedirection at a stretching temperature of 152° C. or less and a drawratio of 4 in machine direction and in transverse direction. Preferably,the stretching temperature mentioned above is at least 2° C., morepreferably at least 3° C. below the melting temperature of the film.

Moreover it is preferred that the film according to the presenttechnology has an electrical breakdown strength EB63% of at least 230kV/mm. The measurement of electrical breakdown strength EB63% followsstandard IEC 60243-part 1 (1988). Further details about electricalbreakdown strength are provided below in the examples.

In addition it is appreciated that the inventive capacitor film has goodoptical properties. Thus it is preferred that capacitor film has a hazeof not more than 15, still more preferred not more than 10 measuredaccording to ASTM D 1003-92. In turn the transparency of the film shallbe rather high. Thus it is preferred that the capacitor film has atransparency of at least 90% measured according to ASTM D 1003-92.

Preferably the polypropylene of the film according to the presenttechnology has low levels of impurities, i.e. low levels of aluminium(Al) residue and/or low levels of silicon residue (Si) and/or low levelsof boron (B) residue. Accordingly the aluminium residues of thepolypropylene can be lowered to a level of 12.00 ppm. On the other handthe properties of the present technology are not detrimentallyinfluenced by the presence of residues. Hence in one preferredembodiment the film according to the present technology comprises apolypropylene which is preferably essentially free of any boron and/orsilicon residues, i.e. residues thereof are not detectable (The analysisof residue contents is defined in the example section). In anotherpreferred embodiment the polypropylene of the film according to thepresent technology comprises boron and/or silicon in detectable amounts,i.e. in amounts of more than 0.10 ppm of boron residues and/or siliconresidues, still more preferably in amounts of more than 0.20 ppm ofboron residues and/or silicon residues, yet more preferably in amountsof more than 0.50 ppm of boron residues and/or silicon residues. Instill another preferred embodiment the polypropylene component of thefilm according to the present technology comprises Al residues in anamount of more than 12.00 ppm, even more preferred in an amount of morethan 20.00 ppm, yet more preferred in an amount of more than 25.00 ppm.In yet another preferred embodiment the polypropylene component of thefilm according to the present technology comprises boron and/or siliconin detectable amounts, i.e. in amounts of more than 0.20 ppm of boronresidues and/or silicon residues, and aluminium residues in an amount ofmore than 12.00 ppm, even more preferred in an amount of more than 20.00ppm and yet more preferred in an amount of more than 25.00 ppm.

Moreover preferably the capacitor film according to the presenttechnology has low levels of impurities, i.e. low levels of aluminium(Al) residue and/or low levels of silicon residue (Si) and/or low levelsof boron (B) residue. Accordingly the aluminium residues of the film canbe lowered to a level of 12.00 ppm. On the other hand the properties ofthe present technology are not detrimentally influenced by the presenceof residues. Hence in one preferred embodiment the film according to thepresent technology is preferably essentially free of any boron and/orsilicon residues, i.e. residues thereof are not detectable (The analysisof residue contents is defined in the example section). In anotherpreferred embodiment the film according to the present technologycomprises boron and/or silicon in detectable amounts, i.e. in amounts ofmore than 0.10 ppm of boron residues and/or silicon residues, still morepreferably in amounts of more than 0.20 ppm of boron residues and/orsilicon residues, yet more preferably in amounts of more than 0.50 ppmof boron residues and/or silicon residues. In still another preferredembodiment the film according to the present technology comprises Alresidues in an amount of more than 12.00 ppm, even more preferred in anamount of more than 20.00 ppm and yet more preferred in an amount ofmore than 25.00 ppm. In yet another preferred embodiment the filmaccording to the present technology comprises boron and/or silicon indetectable amounts, i.e. in amounts of more than 0.20 ppm of boronresidues and/or silicon residues, and aluminium residues in an amount ofmore than 12.00 ppm, even more preferred in an amount of more than 20.00ppm and yet more preferred in an amount of more than 25.00 ppm.

In a preferred embodiment the polypropylene as defined above (andfurther defined below) is preferably unimodal. In another preferredembodiment the polypropylene as defined above (and further definedbelow) is preferably multimodal, more preferably bimodal.

“Multimodal” or “multimodal distribution” describes a frequencydistribution that has several relative maxima (contrary to unimodalhaving only one maximum). In particular, the expression “modality of apolymer” refers to the form of its molecular weight distribution (MWD)curve, i.e. the appearance of the graph of the polymer weight fractionas a function of its molecular weight. If the polymer is produced in thesequential step process, i.e. by utilizing reactors coupled in series,and using different conditions in each reactor, the different polymerfractions produced in the different reactors each have their ownmolecular weight distribution which may considerably differ from oneanother. The molecular weight distribution curve of the resulting finalpolymer can be seen at a super-imposing of the molecular weightdistribution curves of the polymer fraction which will, accordingly,show a more distinct maxima, or at least be distinctively broadenedcompared with the curves for individual fractions.

A polymer showing such molecular weight distribution curve is calledbimodal or multimodal, respectively.

In case the polypropylene of the capacitor film is not unimodal it ispreferably bimodal.

The polypropylene of the film according to the present technology can bea homopolymer or a copolymer. In case the polypropylene is unimodal thepolypropylene is preferably a polypropylene homopolymer. In turn in casethe polypropylene is multimodal, more preferably bimodal, thepolypropylene can be a polypropylene homopolymer as well as apolypropylene copolymer. However it is in particular preferred that incase the polypropylene is multimodal, more preferably bimodal, thepolypropylene is a polypropylene homopolymer. Furthermore it ispreferred that at least one of the fractions of the multimodalpolypropylene is a short-chain branched polypropylene, preferably ashort-chain branched polypropylene homopolymer, as defined above.

The polypropylene of the capacitor film according to the presenttechnology is most preferably a unimodal polypropylene homopolymer.

The expression polypropylene homopolymer as used in the presenttechnology relates to a polypropylene that consists substantially, i.e.of at least 97 wt %, preferably of at least 99 wt %, and most preferablyof at least 99.8 wt % of propylene units. In a preferred embodiment onlypropylene units in the polypropylene homopolymer are detectable. Thecomonomer content can be measured with FT infrared spectroscopy. Furtherdetails are provided below in the examples.

In case the polypropylene of the film according to the presenttechnology is a multimodal or bimodal polypropylene copolymer, it ispreferred that the comonomer is ethylene. However, also other comonomersknown in the art are suitable. Preferably, the total amount ofcomonomer, more preferably ethylene, in the propylene copolymer is up to30 wt %, more preferably up to 25 wt %.

In a preferred embodiment, the multimodal or bimodal polypropylenecopolymer is a polypropylene copolymer comprising a polypropylenehomopolymer matrix being a short chain branched polypropylene as definedabove and an ethylene-propylene rubber (EPR).

The polypropylene homopolymer matrix can be unimodal or multimodal, i.e.bimodal. However it is preferred that polypropylene homopolymer matrixis unimodal.

Preferably, the ethylene-propylene rubber (EPR) in the total multimodalor bimodal polypropylene copolymer is up to 50 wt %. More preferably theamount of ethylene-propylene rubber (EPR) in the total multimodal orbimodal polypropylene copolymer is in the range of 10 to 40 wt %, stillmore preferably in the range of 10 to 30 wt %.

In addition, it is preferred that the multimodal or bimodalpolypropylene copolymer comprises a polypropylene homopolymer matrixbeing a short chain branched polypropylene as defined above and anethylene-propylene rubber (EPR) with an ethylene-content of up to 50 wt%.

In addition, it is preferred that the polypropylene as defined above isproduced in the presence of the catalyst as defined below. Furthermore,for the production of the polypropylene as defined above, the process asstated below is preferably used.

The polypropylene of the capacitor film according to the presenttechnology has been in particular obtained by a new catalyst system.This new catalyst system comprises a symmetric catalyst, whereby thecatalyst system has a porosity of less than 1.40 ml/g, more preferablyless than 1.30 ml/g and most preferably less than 1.00 ml/g. Theporosity has been measured according to DIN 66135 (N₂). In anotherpreferred embodiment the porosity is not detectable when determined withthe method applied according to DIN 66135 (N₂).

A symmetric catalyst according to the present technology is ametallocene compound having a C₂-symetry. Preferably the C₂-symetricmetallocene comprises two identical organic ligands, still morepreferably comprises only two organic ligands which are identical, yetmore preferably comprises only two organic ligands which are identicaland linked via a bridge.

Said symmetric catalyst is preferably a single site catalyst (SSC).

Due to the use of the catalyst system with a very low porositycomprising a symmetric catalyst the manufacture of the above definedshort-chain branched polypropylene is possible.

Furthermore it is preferred, that the catalyst system has a surface areaof lower than 25 m²/g, yet more preferred lower than 20 m²/g, still morepreferred lower than 15 m²/g, yet still lower than 10 m²/g and mostpreferred lower than 5 m²/g. The surface area according to the presenttechnology is measured according to ISO 9277 (N₂).

It is in particular preferred that the catalytic system according to thepresent technology comprises a symmetric catalyst, i.e. a catalyst asdefined above and in further detail below, and has porosity notdetectable when applying the method according to DIN 66135 (N₂) and hasa surface area measured according to ISO 9277 (N₂) of less than 5 m²/g.

Preferably the symmetric catalyst compound, i.e. the C₂-symetricmetallocene, has the formula (I):(Cp)₂R₁MX₂  (I);

-   -   wherein:    -   M is Zr, Hf or Ti, more preferably Zr; and    -   X is independently a monovalent anionic ligand, such as        σ-ligand;    -   R is a bridging group linking the two Cp ligands;    -   Cp is an organic ligand selected from the group consisting of        unsubstituted cyclopenadienyl, unsubstituted indenyl,        unsubstituted tetrahydroindenyl, unsubstituted fluorenyl,        substituted cyclopenadienyl, substituted indenyl, substituted        tetrahydroindenyl, and substituted fluorenyl;    -   with the proviso that both Cp-ligands are selected from the        above stated group and both Cp-ligands are chemically the same,        i.e. are identical.

The term “σ-ligand” is understood in the whole description in a knownmanner, i.e. a group bonded to the metal at one or more places via asigma bond. A preferred monovalent anionic ligand is halogen, inparticular chlorine (Cl).

Preferably, the symmetric catalyst is of formula (I) indicated above,wherein:

-   -   M is Zr; and    -   each X is Cl.

Preferably both identical Cp-ligands are substituted.

The optional one or more substituent(s) bonded to cyclopenadienyl,indenyl, tetrahydroindenyl, or fluorenyl may be selected from a groupincluding halogen, hydrocarbyl (e.g. C₁-C₂₀-alkyl, C₂-C₂₀-alkenyl,C₂-C₂₀-alkynyl, C₃-C₁₂-cycloalkyl, C₆-C₂₀-aryl or C₇-C₂₀-arylalkyl),C₃-C₁₂-cycloalkyl which contains 1, 2, 3 or 4 heteroatom(s) in the ringmoiety, C₆-C₂₀-heteroaryl, C₁-C₂₀-haloalkyl, —SiR″₃, —OSiR″₃, —SR″,—PR″₂ and —NR″₂, wherein each R″ is independently a hydrogen orhydrocarbyl, e.g. C₁-C₂₀-alkyl, C₂-C₂₀-alkenyl, C₂-C₂₀-alkynyl,C₃-C₁₂-cycloalkyl or C₆-C₂₀-aryl.

More preferably both identical Cp-ligands are indenyl moieties whereineach indenyl moiety bear one or two substituents as defined above. Morepreferably each of the identical Cp-ligands is an indenyl moiety bearingtwo substituents as defined above, with the proviso that thesubstituents are chosen in such are manner that both Cp-ligands are ofthe same chemical structure, i.e both Cp-ligands have the samesubstituents bonded to chemically the same indenyl moiety.

Still more preferably both identical Cp's are indenyl moieties whereinthe indenyl moieties comprise at least at the five membered ring of theindenyl moiety, more preferably at 2-position, a substituent selectedfrom the group consisting of alkyl, such as C₁-C₆ alkyl, e.g. methyl,ethyl, isopropyl, and trialkyloxysiloxy, wherein each alkyl isindependently selected from C₁-C₆ alkyl, such as methyl or ethyl, withproviso that the indenyl moieties of both Cp are of the same chemicalstructure, i.e both Cp-ligands have the same substituents bonded tochemically the same indenyl moiety.

Still more preferred both identical Cp are indenyl moieties wherein theindenyl moieties comprise at least at the six membered ring of theindenyl moiety, more preferably at 4-position, a substituent selectedfrom the group consisting of a C₆-C₂₀ aromatic ring moiety, such asphenyl or naphthyl, preferably phenyl, which is optionally substitutedwith one or more substitutents, such as C₁-C₆ alkyl, and aheteroaromatic ring moiety, with proviso that the indenyl moieties ofboth Cp are of the same chemical structure, i.e both Cp-ligands have thesame substituents bonded to chemically the same indenyl moiety.

Yet more preferably both identical Cp are indenyl moieties wherein theindenyl moieties comprise at the five membered ring of the indenylmoiety, more preferably at 2-position, a substituent and at the sixmembered ring of the indenyl moiety, more preferably at 4-position, afurther substituent, wherein the substituent of the five membered ringis selected from the group consisting of alkyl, such as C₁-C₆ alkyl,e.g. methyl, ethyl, isopropyl, and trialkyloxysiloxy and the furthersubstituent of the six membered ring is selected from the groupconsisting of a C₆-C₂₀ aromatic ring moiety, such as phenyl or naphthyl,preferably phenyl, which is optionally substituted with one or moresubstituents, such as C₁-C₆ alkyl, and a heteroaromatic ring moiety,with proviso that the indenyl moieties of both Cp's are of the samechemical structure, i.e both Cp-ligands have the same substituentsbonded to chemically the same indenyl moiety.

Concerning the moiety “R” it is preferred that “R” has the formula (II)—Y(R′)₂—  (II);

-   -   wherein:    -   Y is C, Si or Ge; and    -   R′ is C₁ to C₂₀ alkyl, C₆-C₁₂ aryl, or C₇-C₁₂ arylalkyl or        trimethylsilyl.

In case both Cp-ligands of the symmetric catalyst as defined above, inparticular case of two indenyl moieties, are linked with a bridge memberR, the bridge member R is typically placed at 1-position. The bridgemember R may contain one or more bridge atoms selected from e.g. C, Siand/or Ge, preferably from C and/or Si. One preferable bridge R is—Si(R′)₂—, wherein R′ is selected independently from one or more of e.g.trimethylsilyl, C₁-C₁₀ alkyl, C₁-C₂₀ alkyl, such as C₆-C₁₂ aryl, orC₇-C₄₀, such as C₇-C₁₂ arylalkyl, wherein alkyl as such or as part ofarylalkyl is preferably C₁-C₆ alkyl, such as ethyl or methyl, preferablymethyl, and aryl is preferably phenyl. The bridge —Si(R′)₂— ispreferably e.g. —Si(C₁-C₆ alkyl)₂-, —Si(phenyl)₂- or —Si(C₁-C₆alkyl)(phenyl)-, such as —Si(Me)₂-.

In a preferred embodiment the symmetric catalyst, i.e. the C₂-symetricmetallocene, is defined by the formula (III):(Cp)₂R₁ZrCl₂  (III)

-   -   wherein:    -   both Cp coordinate to M and are selected from the group        consisting of unsubstituted cyclopenadienyl, unsubstituted        indenyl, unsubstituted tetrahydroindenyl, unsubstituted        fluorenyl, substituted cyclopenadienyl, substituted indenyl,        substituted tetrahydroindenyl, and substituted fluorenyl;    -   with the proviso that both Cp-ligands are chemically the same,        i.e. are identical; and    -   R is a bridging group linking two ligands L;    -   wherein R is defined by the formula (II):        —Y(R′)₂—  (II)    -   wherein:    -   Y is C, Si or Ge; and    -   R′ is C₁ to C₂₀ alkyl, C₆-C₁₂ aryl, trimethylsilyl, or C₇-C₁₂        arylalkyl.

More preferably the symmetric catalyst is defined by the formula (III),wherein both Cp are selected from the group consisting of substitutedcyclopenadienyl, substituted indenyl, substituted tetrahydroindenyl, andsubstituted fluorenyl.

In a preferred embodiment the symmetric catalyst isdimethylsilyl(2-methyl-4-phenyl-indenyl)₂zirkonium dichloride(dimethylsilandiylbis(2-methyl-4-phenyl-indenyl)zirkonium dichloride).More preferred said symmetric catalyst is non-silica supported.

The above described symmetric catalyst components are prepared accordingto the methods described in WO 01/48034.

It is in particular preferred that the symmetric catalyst is obtainableby the emulsion solidification technology as described in WO 03/051934.This document is herewith included in its entirety by reference. Hencethe symmetric catalyst is preferably in the form of solid catalystparticles, obtainable by a process comprising the steps of:

-   -   a. preparing a solution of one or more symmetric catalyst        components;    -   b. dispersing said solution in a solvent immiscible therewith to        form an emulsion in which said one or more catalyst components        are present in the droplets of the dispersed phase;    -   c. solidifying said dispersed phase to convert said droplets to        solid particles and optionally recovering said particles to        obtain said catalyst.

Preferably a solvent, more preferably an organic solvent, is used toform said solution. Still more preferably the organic solvent isselected from the group consisting of a linear alkane, cyclic alkane,linear alkene, cyclic alkene, aromatic hydrocarbon andhalogen-containing hydrocarbon.

Moreover the immiscible solvent forming the continuous phase is an inertsolvent, more preferably the immiscible solvent comprises a fluorinatedorganic solvent and/or a functionalized derivative thereof, still morepreferably the immiscible solvent comprises a semi-, highly- orperfluorinated hydrocarbon and/or a functionalized derivative thereof.It is in particular preferred, that said immiscible solvent comprises aperfluorohydrocarbon or a functionalized derivative thereof, preferablyC₃-C₃₀ perfluoroalkanes, -alkenes or -cycloalkanes, more preferredC₄-C₁₀ perfluoro-alkanes, -alkenes or -cycloalkanes, particularlypreferred perfluorohexane, perfluoroheptane, perfluorooctane orperfluoro (methylcyclohexane) or a mixture thereof.

Furthermore it is preferred that the emulsion comprising said continuousphase and said dispersed phase is a bi-or multiphasic system as known inthe art. An emulsifier may be used for forming the emulsion. After theformation of the emulsion system, said catalyst is formed in situ fromcatalyst components in said solution.

In principle, the emulsifying agent may be any suitable agent whichcontributes to the formation and/or stabilization of the emulsion andwhich does not have any adverse effect on the catalytic activity of thecatalyst. The emulsifying agent may e.g. be a surfactant based onhydrocarbons optionally interrupted with (a) heteroatom(s), preferablyhalogenated hydrocarbons optionally having a functional group,preferably semi-, highly- or perfluorinated hydrocarbons as known in theart. Alternatively, the emulsifying agent may be prepared during theemulsion preparation, e.g. by reacting a surfactant precursor with acompound of the catalyst solution. Said surfactant precursor may be ahalogenated hydrocarbon with at least one functional group, e.g. ahighly fluorinated C₁ to C₃₀ alcohol, which reacts e.g. with acocatalyst component, such as aluminoxane.

In principle any solidification method can be used for forming the solidparticles from the dispersed droplets. According to one preferableembodiment the solidification is effected by a temperature changetreatment. Hence the emulsion subjected to gradual temperature change ofup to 10° C./min, preferably 0.5 to 6° C./min and more preferably 1 to5° C./min. Even more preferred the emulsion is subjected to atemperature change of more than 40° C., preferably more than 50° C.within less than 10 seconds, preferably less than 6 seconds.

The recovered particles have preferably an average size range of 5 to200 μm, more preferably 10 to 100 μm.

Moreover, the form of solidified particles have preferably a sphericalshape, a predetermined particles size distribution and a surface area asmentioned above of preferably less than 25 m²/g, still more preferablyless than 20 m²/g, yet more preferably less than 15 m²/g, yet still morepreferably less than 10 m²/g and most preferably less than 5 m²/g,wherein said particles are obtained by the process as described above.

For further details, embodiments and examples of the continuous anddispersed phase system, emulsion formation method, emulsifying agent andsolidification methods reference is made e.g. to the above citedinternational patent application WO 03/051934.

The above described symmetric catalyst components are prepared accordingto the methods described in WO 01/48034.

As mentioned above the catalyst system may further comprise an activatoras a cocatalyst, as described in WO 03/051934, which is enclosed hereinwith reference.

Preferred as cocatalysts for metallocenes and non-metallocenes, ifdesired, are the aluminoxanes, in particular theC₁-C₁₀-alkylaluminoxanes, most particularly methylaluminoxane (MAO).Such aluminoxanes can be used as the sole cocatalyst or together withother cocatalyst(s). Thus besides or in addition to aluminoxanes, othercation complex forming catalysts activators can be used. Said activatorsare commercially available or can be prepared according to the prior artliterature.

Further aluminoxane cocatalysts are described i.a. in WO 94/28034 whichis incorporated herein by reference. These are linear or cyclicoligomers of having up to 40, preferably 3 to 20, —(Al(R′″)O)— repeatunits (wherein R′″ is hydrogen, C₁-C₁₀-alkyl (preferably methyl) orC₆-C₁₈-aryl or mixtures thereof).

The use and amounts of such activators are within the skills of anexpert in the field. As an example, with the boron activators, 5:1 to1:5, preferably 2:1 to 1:2, such as 1:1, ratio of the transition metalto boron activator may be used. In case of preferred aluminoxanes, suchas methylaluminumoxane (MAO), the amount of Al, provided by aluminoxane,can be chosen to provide a molar ratio of Al:transition metal e.g. inthe range of 1 to 10 000, suitably 5 to 8000, preferably 10 to 7000,e.g. 100 to 4000, such as 1000 to 3000. Typically in case of solid(heterogeneous) catalyst the ratio is preferably below 500.

The quantity of cocatalyst to be employed in the catalyst of the presenttechnology is thus variable, and depends on the conditions and theparticular transition metal compound chosen in a manner well known to aperson skilled in the art.

Any additional components to be contained in the solution comprising theorganotransition compound may be added to said solution before or,alternatively, after the dispersing step.

Furthermore, the present technology is related to the use of theabove-defined catalyst system for the production of a polypropyleneaccording to the present technology.

In addition, the present technology is related to the process forproducing the inventive capacitor film comprising the polypropylene,whereby the catalyst system as defined above is employed. Furthermore itis preferred that the process temperature is higher than 60° C.Preferably, the process is a multi-stage process to obtain multimodalpolypropylene as defined above.

Multistage processes include also bulk/gas phase reactors known asmultizone gas phase reactors for producing multimodal propylene polymer.

A preferred multistage process is a “loop-gas phase”-process, such asdeveloped by Borealis A/S, Denmark (known as BORSTAR® technology)described e.g. in patent literature, such as in EP 0 887 379 or in WO92/12182.

Multimodal polymers can be produced according to several processes whichare described, e.g. in WO 92/12182, EP 0 887 379 and WO 97/22633.

A multimodal polypropylene according to the present technology isproduced preferably in a multi-stage process in a multi-stage reactionsequence as described in WO 92/12182. The contents of this document areincluded herein by reference.

It has previously been known to produce multimodal, in particularbimodal, polypropylene in two or more reactors connected in series, i.e.in different steps (a) and (b).

According to the present technology, the main polymerization stages arepreferably carried out as a combination of a bulk polymerization/gasphase polymerization.

The bulk polymerizations are preferably performed in a so-called loopreactor.

In order to produce the multimodal polypropylene according to thepresent technology, a flexible mode is preferred. For this reason, it ispreferred that the composition be produced in two main polymerizationstages in combination of loop reactor/gas phase reactor.

Optionally, and preferably, the process may also comprise aprepolymerization step in a manner known in the field and which mayprecede the polymerization step (a).

If desired, a further elastomeric comonomer component, so calledethylene-propylene rubber (EPR) component as in the present technology,may be incorporated into the obtained polypropylene homopolymer matrixto form a propylene copolymer as defined above. The ethylene-propylenerubber (EPR) component may preferably be produced after the gas phasepolymerization step (b) in a subsequent second or further gas phasepolymerizations using one or more gas phase reactors.

The process is preferably a continuous process.

Preferably, in the process for producing the propylene polymer asdefined above the conditions for the bulk reactor of step (a) may be asfollows:

-   -   the temperature is within the range of 40° C. to 110° C.,        preferably between 60° C. and 100° C., 70 to 90° C.;    -   the pressure is within the range of 20 bar to 80 bar, preferably        between 30 bar to 60 bar;    -   hydrogen can be added for controlling the molar mass in a manner        known per se.

Subsequently, the reaction mixture from the bulk (bulk) reactor (step a)is transferred to the gas phase reactor, i.e. to step (b), whereby theconditions in step (b) are preferably as follows:

-   -   the temperature is within the range of 50° C. to 130° C.,        preferably between 60° C. and 100° C.;    -   the pressure is within the range of 5 bar to 50 bar, preferably        between 15 bar to 35 bar;    -   hydrogen can be added for controlling the molar mass in a manner        known per se.

The residence time can vary in both reactor zones. In one embodiment ofthe process for producing the propylene polymer the residence time inbulk reactor, e.g. loop is in the range 0.5 to 5 hours, e.g. 0.5 to 2hours and the residence time in gas phase reactor will generally be 1 to8 hours.

If desired, the polymerization may be effected in a known manner undersupercritical conditions in the bulk, preferably loop reactor, and/or asa condensed mode in the gas phase reactor.

The process of the present technology or any embodiments thereof aboveenable highly feasible means for producing and further tailoring thepropylene polymer composition within the present technology, e.g. theproperties of the polymer composition can be adjusted or controlled in aknown manner e.g. with one or more of the following process parameters:temperature, hydrogen feed, comonomer feed, propylene feed e.g. in thegas phase reactor, catalyst, the type and amount of an external donor(if used), split between components.

The above process enables very feasible means for obtaining thereactor-made polypropylene as defined above.

The capacitor film can be prepared by conventional drawing processesknown in the art. Accordingly the process for the manufacture of acapacitor film according to the present technology comprises the use ofthe polypropylene as defined herein and its forming into a film,preferably into a cast film. Typically, a cast film is prepared first byextrusion of polypropylene pellets. Prepared cast films may typicallyhave a thickness of 50-100 μm as used for further film stretching.Subsequently, a staple of cast films can be prepared from a number ofcast film sheets to achieve a specific staple thickness, e.g. 700-1000μm. The stretching temperature is typically set to a temperatureslightly below the melting point, e.g. 2-4° C. below the melting point,and the film is stretched at a specific draw ratio in machine directionand transverse direction.

Moreover the present technology is directed to the use of the capacitorfilm as defined herein in a capacitor.

In addition, the present technology is directed to a capacitorcomprising at least on layer comprising a capacitor film as definedherein.

The present technology will now be described in further detail by thefollowing examples.

EXAMPLES 1. Definitions/Measuring Methods

The following definitions of terms and determination methods apply forthe above general description of the present technology as well as tothe below examples unless otherwise defined.

A. Pentad Concentration

For the meso pentad concentration analysis, also referred herein aspentad concentration analysis, the assignment analysis is undertakenaccording to T Hayashi, Pentad concentration, R. Chujo and T. Asakura,Polymer 29 138-43 (1988) and Chujo R, et al., Polymer 35 339 (1994).

B. Multi-branching Index

1. Acquiring the Experimental Data

Polymer is melted at T=180° C. and stretched with the SER UniversalTesting Platform as described below at deformation rates of dε/dt=0.10.3 1.0 3.0 and 10 s⁻¹ in subsequent experiments. The method to acquirethe raw data is described in Sentmanat et al., J. Rheol. 2005, Measuringthe Transient Elongational Rheology of Polyethylene Melts Using the SERUniversal Testing Platform.

Experimental Setup

A Paar Physica MCR300, equipped with a TC30 temperature control unit andan oven CTT600 (convection and radiation heating) and a SERVP01-025extensional device with temperature sensor and a software RHEOPLUS/32v2.66 is used.

Sample Preparation

Stabilized Pellets are compression moulded at 220° C. (gel time 3 min,pressure time 3 min, total moulding time 3+3=6 min) in a mould at apressure sufficient to avoid bubbles in the specimen, cooled to roomtemperature. From such prepared plate of 0.7 mm thickness, stripes of awidth of 10 mm and a length of 18 mm are cut.

Check of the SER Device

Because of the low forces acting on samples stretched to thinthicknesses, any essential friction of the device would deteriorate theprecision of the results and has to be avoided.

In order to make sure that the friction of the device less than athreshold of 5×10−3 mNm (Milli-Newtonmeter) which is required forprecise and correct measurements, following check procedure is performedprior to each measurement:

-   -   The device is set to test temperature (180° C.) for minimum 20        minutes without sample in presence of the clamps    -   A standard test with 0.3 s⁻¹ is performed with the device on        test temperature (180° C.)    -   The torque (measured in mNm) is recorded and plotted against        time    -   The torque must not exceed a value of 5×10⁻³ mNm to make sure        that the friction of the device is in an acceptably low range        Conducting the Experiment

The device is heated for min. 20 min to the test temperature (180° C.measured with the thermocouple attached to the SER device) with clampsbut without sample. Subsequently, the sample (0.7×10×18 mm), prepared asdescribed above, is clamped into the hot device. The sample is allowedto melt for 2 minutes +/−20 seconds before the experiment is started.

During the stretching experiment under inert atmosphere (nitrogen) atconstant Hencky strain rate, the torque is recorded as function of timeat isothermal conditions (measured and controlled with the thermocoupleattached to the SER device).

After stretching, the device is opened and the stretched film (which iswinded on the drums) is inspected. Homogenous extension is required. Itcan be judged visually from the shape of the stretched film on the drumsif the sample stretching has been homogenous or not. The tape must mewound up symmetrically on both drums, but also symmetrically in theupper and lower half of the specimen.

If symmetrical stretching is confirmed hereby, the transientelongational viscosity calculates from the recorded torque as outlinedbelow.

2. Evaluation

For each of the different strain rates dε/dt applied, the resultingtensile stress growth function η_(E) ⁺(dε/dt, t) is plotted against thetotal Hencky strain ε to determine the strain hardening behaviour of themelt, see FIG. 1.

In the range of Hencky strains between 1.0 and 3.0, the tensile stressgrowth function η_(E) ⁺ can be well fitted with a function:η_(E) ⁺({dot over (ε)},ε)=c ₁·ε^(c) ² ;

-   -   where c₁ and c₂ are fitting variables. Such derived c₂ is a        measure for the strain hardening behavior of the melt and called        Strain Hardening Index SHI.

Dependent on the polymer architecture, SHI can:

-   -   be independent of the strain rate (linear materials, Y— or        H-structures)    -   increase with strain rate (short chain-, hyper- or        multi-branched structures).

This is illustrated in FIG. 2.

For polyethylene, linear (HDPE), short-chain branched (LLDPE) andhyperbranched structures (LDPE) are well known and hence they are usedto illustrate the structural analytics based on the results onextensional viscosity. They are compared with a polypropylene with Y andH-structures with regard to their change of the strain-hardeningbehavior as function of strain rate, see FIG. 2 and Table 1.

To illustrate the determination of SHI at different strain rates as wellas the multi-branching index (MBI) four polymers of known chainarchitecture are examined with the analytical procedure described above.

The first polymer is a H— and Y-shaped polypropylene homopolymer madeaccording to EP 879 830 (“A”). It has a MFR230/2.16 of 2.0 g/10 min, atensile modulus of 1950 MPa and a branching index g′ of 0.7.

The second polymer is a commercial hyperbranched LDPE, Borealis “B”,made in a high pressure process known in the art. It has a MFR190/2.16of 4.5 and a density of 923 kg/m³.

The third polymer is a short chain branched LLDPE, Borealis “C”, made ina low pressure process known in the art. It has a MFR190/2.16 of 1.2 anda density of 919 kg/m³.

The fourth polymer is a linear HDPE, Borealis “D”, made in a lowpressure process known in the art. It has a MFR190/2.16 of 4.0 and adensity of 954 kg/m³.

The four materials of known chain architecture are investigated by meansof measurement of the transient elongational viscosity at 180° C. atstrain rates of 0.10, 0.30, 1.0, 3.0 and 10 s⁻¹. Obtained data(transient elongational viscosity versus Hencky strain) is fitted with afunction:η_(E) ⁺ =c ₁*ε^(c) ² ;

for each of the mentioned strain rates. The parameters c1 and c2 arefound through plotting the logarithm of the transient elongationalviscosity against the logarithm of the Hencky strain and performing alinear fit of this data applying the least square method. The parameterc1 calculates from the intercept of the linear fit of the data lg(η_(E)⁺) versus lg(ε) from:c₁=10^(Intercept);

and c₂ is the strain hardening index (SHI) at the particular strainrate.

This procedure is done for all five strain rates and hence, SHI@0.1 s⁻¹,SHI@0.3 s⁻¹, SHI@1.0 s⁻¹, SHI@3.0 s⁻¹, SHI@10 s⁻¹ are determined, seeFIG. 1.

TABLE 1 SHI-values short- Y and H multi- chain lg branched branchedbranched linear dε/dt (dε/dt) Property A B C D 0.1 −1.0 SHI@0.1 s⁻¹ 2.05— 0.03 0.03 0.3 −0.5 SHI@0.3 s⁻¹ — 1.36 0.08 0.03 1 0.0 SHI@1.0 s⁻¹ 2.191.65 0.12 0.11 3 0.5 SHI@3.0 s⁻¹ — 1.82 0.18 0.01 10 1.0 SHI@10 s⁻¹ 2.142.06 — —

From the strain hardening behaviour measured by the values of the SHI@ 1s⁻¹ one can already clearly distinguish between two groups of polymers:Linear and short-chain branched have a SHI@1 s⁻¹ significantly smallerthan 0.30. In contrast, the Y and H-branched as well as hyperbranchedmaterials have a SHI@1 s⁻¹ significantly larger than 0.30.

In comparing the strain hardening index at those five strain rates {dotover (ε)}_(H) of 0.10, 0.30, 1.0, 3.0 and 10 s⁻¹, the slope of SHI asfunction of the logarithm of {dot over (ε)}_(H), lg({dot over (ε)}_(H))is a characteristic measure for multi-branching. Therefore, amulti-branching index (MBI) is calculated from the slope of a linearfitting curve of SHI versus lg({dot over (ε)}_(H)):SHI({dot over (ε)}_(H))=c3+MBI*lg({dot over (ε)}_(H));

The parameters c3 and MBI are found through plotting the SHI against thelogarithm of the Hencky strain rate lg({dot over (ε)}_(H)) andperforming a linear fit of this data applying the least square method.Please confer to FIG. 2.

TABLE 2 MBI-values Y and H short-chain Property branched A multibranchedB branched C linear D MBI 0.04 0.45 0.10 0.01

The multi-branching index MBI allows now to distinguish between Y orH-branched polymers which show a MBI smaller than 0.05 and hyperbranchedpolymers which show a MBI larger than 0.15. Further, it allows todistinguish between short-chain branched polymers with MBI larger than0.10 and linear materials which have a MBI smaller than 0.10.

Similar results can be observed when comparing different polypropylenes,i.e. polypropylenes with rather high branched structures have higher SHIand MBI-values, respectively, compared to their linear and short-chaincounterparts. Similar to the linear low density polyethylenes the newdeveloped polypropylenes show a certain degree of short-chain branching.However the polypropylenes according to the instant technology areclearly distinguished in the SHI and MBI-values when compared to knownlinear low density polyethylenes. Without being bound on this theory, itis believed, that the different SHI and MBI-values are the result of adifferent branching architecture. For this reason the new found branchedpolypropylenes according to the present technology are designated asshort-chain branched.

Combining both, strain hardening index and multi-branching index, thechain architecture can be assessed as indicated in Table 3:

Table 3: Strain Hardening Index (SHI) and Multi-branching Index (MBI)for various chain architectures

TABLE 3 Strain Hardening Index (SHI) and Multi-branching Index (MBI) forvarious chain architectures Y and H short-chain Property branchedMulti-branched branched linear SHI@1.0 s⁻¹ >0.30 >0.30 ≦0.30 ≦0.30 MBI≦0.10 >0.10 >0.10 ≦0.10C. Elementary Analysis

The below described elementary analysis is used for determining thecontent of elementary residues which are mainly originating from thecatalyst, especially the Al—, B—, and Si-residues in the polymer. SaidAl—, B— and Si-residues can be in any form, e.g. in elementary or ionicform, which can be recovered and detected from polypropylene using thebelow described ICP-method. The method can also be used for determiningthe Ti-content of the polymer. It is understood that also other knownmethods can be used which would result in similar results.

ICP-Spectrometry (Inductively Coupled Plasma Emission)

ICP-instrument: The instrument for determination of Al—, B— andSi-content is ICP Optima 2000 DV, PSN 620785 (supplier Perkin ElmerInstruments, Belgium) with software of the instrument.

Detection limits are 0.10 ppm (Al), 0.10 ppm (B), 0.10 ppm (Si).

The polymer sample was first ashed in a known manner, then dissolved inan appropriate acidic solvent. The dilutions of the standards for thecalibration curve are dissolved in the same solvent as the sample andthe concentrations chosen so that the concentration of the sample wouldfall within the standard calibration curve.

-   -   ppm: means parts per million by weight;    -   Ash content: Ash content is measured according to ISO        3451-1 (1997) standard.        Calculated Ash, Al—Si— and B-Content:

The ash and the above listed elements, Al and/or Si and/or B can also becalculated form a polypropylene based on the polymerization activity ofthe catalyst as exemplified in the examples. These values would give theupper limit of the presence of said residues originating form thecatalyst.

Thus the estimate catalyst residue is based on catalyst composition andpolymerization productivity, catalyst residues in the polymer can beestimated according to:Total catalyst residues[ppm]=1/productivity[kg _(pp)/g _(catalyst)]×100;Al residues[ppm]=w _(Al,catalyst)[%]×total catalyst residues[ppm]/100;Zr residues[ppm]=w _(Zr,catalyst)[%]×total catalyst residues[ppm]/100;

(Similar calculations apply also for B, Cl and Si residues).

Chlorine residues content: The content of Cl-residues is measured fromsamples in the known manner using X-ray fluorescence (XRF) spectrometry.The instrument was X-ray fluorescention Philips PW2400, PSN 620487,(Supplier: Philips, Belgium) software X47. Detection limit for Cl is 1ppm.

D. Further Measuring Methods

Particle size distribution: Particle size distribution is measured viaCoulter Counter LS 200 at room temperature with n-heptane as medium.

NMR

NMR-spectroscopy measurements:

The ¹³C-NMR spectra of polypropylenes were recorded on Bruker 400 MHzspectrometer at 130° C. from samples dissolved in1,2,4-trichlorobenzene/benzene-d6 (90/10 w/w). For the pentad analysisthe assignment is done according to the methods described in literature:(T. Hayashi, Y. Inoue, R. Chüjö, and T. Asakura, Polymer 29 138-43(1988) and Chujo R, et al, Polymer 35 339 (1994).

The NMR-measurement was used for determining the mmmm pentadconcentration in a manner well known in the art.

Number average molecular weight (M_(n)), weight average molecular weight(M_(w)) and molecular weight distribution (MWD) are determined by sizeexclusion chromatography (SEC) using Waters Alliance GPCV 2000instrument with online viscometer. The oven temperature is 140° C.Trichlorobenzene is used as a solvent (ISO 16014).

The xylene solubles (XS, wt.-%): Analysis according to the known method:2.0 g of polymer is dissolved in 250 ml p-xylene at 135° C. underagitation. After 30±2 minutes the solution is allowed to cool for 15minutes at ambient temperature and then allowed to settle for 30 minutesat 25±0.5° C. The solution is filtered and evaporated in nitrogen flowand the residue dried under vacuum at 90° C. until constant weight isreached.

-   -   XS %=(100×m₁×v₀)/(m₀×v₁); wherein    -   m₀=initial polymer amount (g);    -   m₁=weight of residue (g);    -   v₀=initial volume (ml);    -   V₁=volume of analyzed sample (ml).

Melting temperature Tm, crystallization temperature Tc, and the degreeof crystallinity: measured with Mettler TA820 differential scanningcalorimetry (DSC) on 5-10 mg samples. Both crystallization and meltingcurves were obtained during 10° C./min cooling and heating scans between30° C. and 225° C. Melting and crystallization temperatures were takenas the peaks of endotherms and exotherms.

Also the melt- and crystallization enthalpy (Hm and Hc) were measured bythe DSC method according to ISO 11357-3.

MFR₂: measured according to ISO 1133 (230° C., 2.16 kg load).

Comonomer content is measured with Fourier transform infraredspectroscopy (FTIR) calibrated with ¹³C-NMR. When measuring the ethylenecontent in polypropylene, a thin film of the sample (thickness about 250mm) was prepared by hot-pressing. The area of —CH₂-absorption peak(800-650 cm⁻¹) was measured with Perkin Elmer FTIR 1600 spectrometer.The method was calibrated by ethylene content data measured by ¹³C-NMR.

Stiffness Film TD (transversal direction), Stiffness Film MD (machinedirection), Elongation at break TD and Elongation at break MD: these aredetermined according to ISO527-3 (cross head speed: 1 mm/min).

Haze and transparency: are determined: ASTM D1003-92.

Intrinsic viscosity: is measured according to DIN ISO 1628/1, October1999 (in Decalin at 135° C.).

Porosity: is measured according to DIN 66135.

Surface area: is measured according to ISO 9277.

Stepwise Isothermal Segregation Technique (SIST): The isothermalcrystallisation for SIST analysis was performed in a Mettler TA820 DSCon 3±0.5 mg samples at decreasing temperatures between 200° C. and 105°C.

-   -   (i) The samples were melted at 225° C. for 5 min.,    -   (ii) then cooled with 80° C./min to 145° C.    -   (iii) held for 2 hours at 145° C.,    -   (iv) then cooled with 80° C./min to 135° C.    -   (v) held for 2 hours at 135° C.,    -   (vi) then cooled with 80° C./min to 125° C.    -   (vii) held for 2 hours at 125° C.,    -   (viii) then cooled with 80° C./min to 115° C.    -   (ix) held for 2 hours at 115° C.,    -   (x) then cooled with 80° C./min to 105° C.    -   (xi) held for 2 hours at 105° C.

After the last step the sample was cooled down to ambient temperature,and the melting curve was obtained by heating the cooled sample at aheating rate of 110° C./min up to 200° C. All measurements wereperformed in a nitrogen atmosphere. The melt enthalpy is recorded asfunction of temperature and evaluated through measuring the meltenthalpy of fractions melting within temperature intervals as indicatedfor example E 1 in the table 8 and FIG. 5.

The melting curve of the material crystallised this way can be used forcalculating the lamella thickness distribution according toThomson-Gibbs equation (Eq 1.).

$\begin{matrix}{{T_{m} = {T_{0}\left( {1 - \frac{2\;\sigma}{\Delta\;{H_{0} \cdot L}}} \right)}};} & (1)\end{matrix}$

-   -   where T₀=457K, ΔH₀=184×10⁶ J/m³, σ=0.0496 J/m² and L is the        lamella thickness.        Electrical Breakdown Strength (EB63%)

It follows standard IEC 60243-part 1 (1988).

The method describes a way to measure the electrical breakdown strengthfor insulation materials on compression moulded plaques.

-   -   Definition:

${{{Eb}\text{:}\mspace{14mu} E_{b}} = \frac{U_{b}}{d}};$

-   -   The electrical field strength in the test sample at which        breakdown occurs. In homogeneous plaques and films this        corresponds to the electrical electrical breakdown strength        divided by the thickness of the plaque/film (d), unit: kV/mm.

The electrical breakdown strength is determined at 50 Hz within a highvoltage cabinet using metal rods as electrodes as described inIEC60243-1 (4.1.2). The voltage is raised over the film/plaque at 2 kV/suntil a breakdown occurs.

3. Examples Inventive Example 1 (E 1)

Catalyst Preparation

The catalyst was prepared as described in example 5 of WO 03/051934,with the Al— and Zr-ratios as given in said example (Al/Zr=250).

Catalyst Characteristics:

Al— and Zr— content were analyzed via above mentioned method to 36.27wt.-% Al and 0.42%-wt. Zr. The average particle diameter (analyzed viaCoulter counter) is 20 μm and particle size distribution is shown inFIG. 3.

Polymerization

A 5 liter stainless steel reactor was used for propylenepolymerizations. 1100 g of liquid propylene (Borealis polymerizationgrade) was fed to reactor. 0.2 ml triethylaluminum (100%, purchased fromCrompton) was fed as a scavenger and 15 mmol hydrogen (quality 6.0,supplied by Åga) as chain transfer agent. Reactor temperature was set to30° C. 29.1 mg catalyst were flushed into to the reactor with nitrogenoverpressure. The reactor was heated up to 70° C. in a period of about14 minutes. Polymerization was continued for 50 minutes at 70° C., thenpropylene was flushed out, 5 mmol hydrogen were fed and the reactorpressure was increased to 20 bars by feeding (gaseous-) propylene.Polymerization continued in gas-phase for 144 minutes, then the reactorwas flashed, the polymer was dried and weighted.

Polymer yield was weighted to 901 g, that equals a productivity of 31kg_(PP)/g_(catalyst). 1000 ppm of a commercial stabilizer Irganox B 215(FF) (Ciba) have been added to the powder. The powder has been meltcompounded with a Prism TSE16 lab kneader at 250 rpm at a temperature of220-230° C.

Inventive Example 2 (E 2)

A catalyst as used in I1 has been used.

A 5 liter stainless steel reactor was used for propylenepolymerizations. 1100 g of liquid propylene (Borealis polymerizationgrade) was fed to reactor. 0.5 ml triethylaluminum (100%, purchased fromCrompton) was fed as a scavenger and 50 mmol hydrogen (quality 6.0,supplied by Åga) as chain transfer agent. Reactor temperature was set to30° C. 19.9 mg catalyst were flushed into to the reactor with nitrogenoverpressure. The reactor was heated up to 70° C. in a period of about14 minutes. Polymerization was continued for 40 minutes at 70° C., thenpropylene was flushed out, the reactor pressure was increased to 20 barsby feeding (gaseous-) propylene. Polymerization continued in gas-phasefor 273 minutes, then the reactor was flashed, the polymer was dried andweighted.

Polymer yield was weighted to 871 g, that equals a productivity of 44kg_(PP)/g_(catalyst). 1000 ppm of a commercial stabilizer Irganox B 215(FF) (Ciba) have been added to the powder. The powder has been meltcompounded with a Prism TSE16 lab kneader at 250 rpm at a temperature of220-230° C.

Comparative Example 1 (CE 1)

A commercial polypropylene homopolymer of Borealis has been used.

Comparative Example 2 (CE 2)

A commercial polypropylene homopolymer of Borealis has been used.

In Tables 4, 5 and 6, the properties of samples CE 1, CE 2, E 1 and E2are summarized.

TABLE 4 Properties of polypropylene according to the present technologyand comparative examples Unit CE 1 CE 2 E 1 E 2 Ash ppm 15 13 85 n.a.MFR g/10′ 2.1 2.1 2 5.3 Mw g/mol 412000 584000 453000 405000 Mw/Mn — 9.98.1 2.8 5.3 XS wt % 1.2 3.5 0.85 0.66 mmmm — 0.95 0.95 Tm ° C. 162 162150.6 150.8 Hm J/g 107 100 99.5 100.1 Tc ° C. 115 113 111.9 111.2 Hc J/g101 94 74.6 92.8 g′ — 1 1 <1 <1 SHI@1.0 s⁻¹ — 0 0 0.15 n.a. MBI — 0 00.20 n.a. Chain qualitative linear linear Short- Short- Architecturechain chain branched branched

TABLE 5 Preparation of the cast film and characterization Cast film withOCS equipment, thickness constant at 90-110 μm. Unit CE 1 CE 2 E 1 E 2Stiffness Film TD MPa 960 756 1011 n.a. Stiffness Film MD MPa 954 7521059 n.a. Elongation at Break TD % 789 792 700 n.a. Elongation at Break% 733 714 691 n.a. MD Transparency % 94 94 94 n.a. Haze % 24.2 19.9 7.8n.a.

TABLE 6 Preparation of BOPP film and characterization VTT Tampere, 4 × 4Orientation Code Unit CE 1 CE 2 E 1 E 2 EB63% kV/mm 210 224 291 388 90%LOWER CONF: kV/mm 197 203 267 349 90% UPPER CONF: kV/mm 223 244 311 425BETA: none 10.4 6.9 8.3 6.5 Stress MD4 MPa 4.3 3.8 3.6 2.7 Stress TD4MPa 3.4 3.1 3.0 2.5 Stiffness Film 4 × 4 MPa 3003 3138 2550 2020 MDStiffness Film 4 × 4 TD MPa 2943 2691 2824 2554 Elongation at Break % 5253 80 62 Film 4 × 4 TD Elongation at Break % 50 60 34 41 Film 4 × 4 MDTm ONSET Film 4 × 4 ° C. 141 136 137 n.a. Tm Film (1^(st) melting ° C.156 158 154 157 4 × 4) Hm Film (1^(st) melting J/g 56 66 70 92 4 × 4) TcFilm 4 × 4 ° C. 111 112 112 114 Hc Film 4 × 4 J/g 80 78 77 90 Tm Film(2^(nd) melting ° C. 167 165 156 154 4 × 4) Hm Film (2^(nd) melting J/g74 73 69 89 4 × 4)

TABLE 7 Preparation of BOPP film and characterization VTT Tampere, 5 × 5Orientation Code Unit E 2 EB63% kV/mm 638 90% LOWER CONF: kV/mm 563 90%UPPER CONF: kV/mm 707 BETA: none 5.6 Stress MD5 MPa 3.5 Stress TD5 MPa3.4 Stiffness Film 5 × 5 MD MPa 2271 Stiffness Film 5 × 5 TD MPa 2445Elongation at Break Film 5 × 5 TD % 39 Elongation at Break Film 5 × 5 MD% 19 Tm ONSET Film 5 × 5 ° C. n.a. Tm Film (1^(st) melting 5 × 5) ° C.152 Hm Film (1^(st) melting 5 × 5) J/g 83 Tc Film 5 × 5 ° C. 109 Hc Film5 × 5 J/g 95 Tm Film (2^(nd) melting 5 × 5) ° C. 153 Hm Film (2^(nd)melting 5 × 5) J/g 100

A biaxially oriented film is prepared as follows:

In the biaxial stretching Device Bruckner Karo IV, film samples areclamped and extended in both, longitudinal and transverse direction, atconstant stretching speed. The length of the sample increases duringstretching in longitudinal direction and the stretch ratio inlongitudinal direction calculates from the ratio of current length overoriginal sample length. Subsequently, the sample is stretched intransverse direction where the width of the sample is increasing. Hence,the stretch ratio calculates from the current width of the sample overthe original width of the sample.

In Table 8 the crystallization behaviour of sample E 1 is determined viastepwise isothermal segregation technique (SIST).

TABLE 8 Results from stepwise isothermal segregation technique (SIST) E1 CE 2 CE 2 Peak ID Range [° C.] H_(m) [J/g] H_(m) [J/g] H_(m) [J/g] 1<110 6.0 0.6 1.0 2 110-120 3.8 1.0 1.4 3 120-130 4.8 2.0 2.6 4 130-14011.4 3.9 4.8 5 140-150 27.5 10.6 12.8 6 150-160 29.2 25.4 32.1 7 160-17016.9 50.7 56.6 8 >170 0.1 37.5 14.3 H_(m) = melting enthalpy

The present technology has now been described in such full, clear,concise and exact terms as to enable a person familiar in the art towhich it pertains, to practice the same. It is to be understood that theforegoing describes preferred embodiments and examples of the presenttechnology and that modifications may be made therein without departingfrom the spirit or scope of the present technology as set forth in theclaims. Moreover, while particular elements, embodiments andapplications of the present technology have been shown and described, itwill be understood, of course, that the present technology is notlimited thereto since modifications can be made by those familiar in theart without departing from the scope of the present disclosure,particularly in light of the foregoing teachings and appended claims.Moreover, it is also understood that the embodiments shown in thedrawings, if any, and as described above are merely for illustrativepurposes and not intended to limit the scope of the present technology,which is defined by the following claims as interpreted according to theprinciples of patent law, including the Doctrine of Equivalents.Further, all references cited herein are incorporated in their entirety.

1. An electrical insulation film comprising a polypropylene material, atleast one of the electrical insulation film and the polypropylenematerial comprising: a) xylene solubles in the range of about 0.5percent to about 1.5 percent by weight; and b) a crystalline fractioncrystallizing in the temperature range of 200 to 105° C. determined bystepwise isothermal segregation technique, said crystalline fractioncomprising a part; wherein, during subsequent melting at a melting rateof 10° C./min, said part melts at or below 140° C. and said partrepresents at least 10 percent by weight of said crystalline fractionand wherein said electrical insulation film is a capacitor film.
 2. Theelectrical insulation film of claim 1, wherein the film has a strainhardening index of at least 0.15 measured at a deformation rate of 1.00s⁻¹ at a temperature of 180° C., further wherein the strain hardeningindex is defined as the slope of the logarithm to the basis 10 of thetensile stress growth function as function of the logarithm to the basis10 of the Hencky strain for the range of the Hencky strains between 1and
 3. 3. The electrical insulation film of claim 1, wherein saidcrystalline fraction represents at least 90 percent by weight of saidpolypropylene material of said capacitor film.
 4. The electricalinsulation film of claim 1, wherein the film is a biaxially orientedfilm.
 5. The electrical insulation film of claim 1, wherein at least oneof the film and the polypropylene material is stretchable in machine andtransverse direction up to a draw ratio of at least 3.5 withoutbreaking.
 6. The electrical insulation film of claim 1, wherein at leastone of the film and the polypropylene material has a draw ratio inmachine and transverse direction of at least 3.5.
 7. The electricalinsulation film of claim 1, wherein at least one of the film and thepolypropylene material has a tensile modulus of at least 1800 MPa at adraw ratio of 4 in machine direction and a draw ratio of 4 in transversedirection, measured according to ISO 527-3 at a cross head speed of 1mm/min.
 8. The electrical insulation film of claim 1, wherein at leastone of the film and the polypropylene material has a stretching stressof at least 2.5 MPa in machine direction and transverse direction at astretching temperature of 152° C. or less and a draw ratio of 4.0 inmachine direction and transverse direction.
 9. The electrical insulationfilm of claim 1, wherein at least one of the film and the polypropylenematerial has a melting point of at least 148° C.
 10. The electricalinsulation film of claim 1, wherein at least one of the film and thepolypropylene material has a multi-branching index of at least 0.15,wherein the multi-branching index is defined as the slope of strainhardening index as function of the logarithm to the basis 10 of theHencky the Hencky strain rate, defined as log(dε/dt) for this, wherein:a) dε/dt is the deformation rate; b) ε is the Hencky strain; and c) thestrain hardening index is measured at a temperature of 180° C.; andwherein the strain hardening index is defined as the slope of thelogarithm to the basis 10 of the tensile stress growth function, definedas log(ηε⁺), as function of the logarithm to the basis 10 of the Henckystrain in the range of the Hencky strains between 1 and
 3. 11. Theelectrical insulation film of claim 1, wherein at least one of the filmand the polypropylene material has a branching index of less than 1.00.12. The electrical insulation film of claim 1, wherein the polypropylenematerial is multimodal.
 13. The electrical insulation film of claim 1,wherein the polypropylene material is unimodal.
 14. The electricalinsulation film of claim 1, wherein the polypropylene material hasmolecular weight distribution of not more than 8.00 measured accordingto ISO
 16014. 15. The electrical insulation film of claim 1, wherein thepolypropylene material has a melt flow rate of up to 10 g/10 minmeasured according to ISO 1
 133. 16. The electrical insulation film ofclaim 1, wherein the polypropylene material has an mmmm pentadconcentration of higher than 94% determined by NMR-spectroscopy.
 17. Theelectrical insulation film of claim 1, wherein the polypropylenematerial has a meso pentad concentration of higher than 94% determinedby NMR-spectroscopy.
 18. The electrical insulation film of claim 1,wherein the polypropylene material is a propylene homopolymer.
 19. Theelectrical insulation film of claim 1, wherein the polypropylenematerial has been produced in the presence of a catalytic systemcomprising metallocene complex, wherein the catalytic system has aporosity of less than 1.40 ml/g measured according to DIN
 66135. 20. Theelectrical insulation film of claim 1, wherein the polypropylenematerial has been produced in the presence of a symmetric metallocenecomplex.
 21. An electrical insulation film comprising a polypropylenematerial, at least one of the electrical insulation film and thepolypropylene material comprising: a) xylene solubles in the range ofabout 0.5 to about 1.5 percent by weight; and b) a crystalline fractioncrystallizing in the temperature range of 200 to 105° C. determined bystepwise isothermal segregation technique, said crystalline fractioncomprising a part; wherein, during subsequent melting at a melting rateof 10° C./min, said part melts at or below the temperature T=Tm−3° C.,wherein Tm is the melting temperature of at least one of said electricalinsulation film and the polypropylene material, and said part representsat least 45 percent by weight of said crystalline fraction, and whereinsaid electrical insulation film is a capacitor film.
 22. The electricalinsulation film of claim 21, wherein the film is a biaxially orientedfilm.
 23. The electrical insulation film of claim 21, wherein at leastone of the film and the polypropylene material is stretchable in machineand transverse direction up to a draw ratio of at least 3.5 withoutbreaking.
 24. The electrical insulation film of claim 21, wherein atleast one of the film and the polypropylene material is has a draw ratioin machine and transverse direction of at least 3.5.
 25. The electricalinsulation film of claim 21, wherein at least one of the film and thepolypropylene material has a tensile modulus of at least 1800 MPa at adraw ratio of 4 in machine direction and a draw ratio of 4 in transversedirection, measured according to ISO 527-3 at a cross head speed of 1mm/min.
 26. The electrical insulation film of claim 21, wherein at leastone of the film and the polypropylene material has a stretching stressof at least 2.5 MPa in machine direction and transverse direction at astretching temperature of 152° C. or less and a draw ratio of 4.0 inmachine direction and transverse direction.
 27. The electricalinsulation film of claim 21, wherein at least one of the film and thepolypropylene material has a melting point of at least 148° C.
 28. Theelectrical insulation film of claim 21, wherein at least one of the filmand the polypropylene material has a multi-branching index of at least0.15, wherein the multi-branching index is defined as the slope ofstrain hardening index as function of the logarithm to the basis 10 ofthe Hencky the Hencky strain rate, defined as log(dε/dt) for this,wherein: a) dε/dt is the deformation rate; b) ε is the Hencky strain;and c) the strain hardening index is measured at a temperature of 180°C.; and wherein the strain hardening index is defined as the slope ofthe logarithm to the basis 10 of the tensile stress growth function,defined as log(ηε⁺), as function of the logarithm to the basis 10 of theHencky strain in the range of the Hencky strains between 1 and
 3. 29.The electrical insulation film of claim 21, wherein at least one of thefilm and the polypropylene material has a branching index of less than1.00.
 30. The electrical insulation film of claim 21, wherein thepolypropylene material is multimodal.
 31. The electrical insulation filmof claim 21, wherein the polypropylene material is unimodal.
 32. Theelectrical insulation film of claim 21, wherein the polypropylenematerial has molecular weight distribution of not more than 8.00measured according to ISO
 16014. 33. The electrical insulation film ofclaim 21, wherein the polypropylene material has a melt flow rate of upto 10 g/10 min measured according to ISO 1
 133. 34. The electricalinsulation film of claim 21, wherein the polypropylene material has anmmmm pentad concentration of higher than 94% determined byNMR-spectroscopy.
 35. The electrical insulation film of claim 21,wherein the polypropylene material has a meso pentad concentration ofhigher than 94% determined by NMR-spectroscopy.
 36. The electricalinsulation film of claim 21, wherein the polypropylene material is apropylene homopolymer.
 37. The electrical insulation film of claim 21,wherein the polypropylene material has been produced in the presence ofa catalytic system comprising metallocene complex, wherein the catalyticsystem has a porosity of less than 1.40 ml/g measured according to DIN66135.
 38. The electrical insulation film of claim 21, wherein thepolypropylene material has been produced in the presence of a symmetricmetallocene complex.
 39. An electrical insulation film comprising apolypropylene material, at least one of the electrical insulation filmand the polypropylene material comprising xylene solubles of about 0.5percent by weight to about 1.5 percent by weight, wherein saidelectrical insulation film has a strain hardening index of at least 0.15measured at a deformation rate of 1.00 s⁻¹ at a temperature of 180° C.,the strain hardening index defined as the slope of the logarithm to thebasis 10 of the tensile stress growth function as function of thelogarithm to the basis 10 of the Hencky strain for the range of theHencky strains between 1 and 3, and further wherein said electricalinsulation film is a capacitor film.
 40. The electrical insulation filmof claim 39, wherein at least one of the film and the polypropylenematerial further comprises a crystalline fraction crystallizing in thetemperature range of 200 to 105° C. determined by stepwise isothermalsegregation technique, said crystalline fraction comprising a part;wherein, during subsequent melting at a melting rate of 10° C./min, saidpart melts at or below 140° C., fraction, and said part represents atleast 20 percent by weight of said crystalline fraction.
 41. Theelectrical insulation film of claim 39, wherein at least one of the filmand the polypropylene material further comprises a crystalline fractioncrystallizing in the temperature range of 200 to 105° C. determined bystepwise isothermal segregation technique, said crystalline fractioncomprising a part; wherein, during subsequent melting at a melting rateof 10° C./min, said part melts at or below the temperature T=Tm−3° C.,wherein Tm is the melting temperature of at least one of said electricalinsulation film and the polypropylene material, and said part representsat least 50 percent by weight of said crystalline fraction.